Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Civil, Construction, and Environmental Engineering


An extensive review of the literature on design stresses in silos revealed that limiting stress analysis is traditionally used in the design of silos for static lateral stresses, and that overpressures due to the unloading process are allowed for by empirical overpressure factors. It is hypothesized that dilation (volume increase due to shear strain) of the stored material may be a rational explanation for overpressures. Tests in a specially constructed triaxial apparatus indicate that maize, wheat and barley dilate during standard triaxial shear tests, whereas oats, which has higher void ratios, does not. The tests also show that the Mohr failure envelopes are not linear, as normally assumed, but are concave downwards. General expressions for the compression loading tangent modulus and the Mohr failure envelope are developed, and the parameters for the four grains, each at three bulk densities, evaluated. For the maize, wheat and barley, the highest friction angles and initial tangent moduli and the lowest failure strains occur at the intermediate bulk densities. Standard and constant volume tests indicate that stress-strain characteristics are more dependent upon grain packing and stress history, whereas frictional behavior is more dependent upon the geometry and surface roughness of the individual grains.



Digital Repository @ Iowa State University,

Copyright Owner

David Llewellyn Owen Smith



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102 pages